Paper 3 Exam Questions

Question 1

What is reflux?

Answer 1

Mixture of liquids is heated to boiling point over a long period of time

Question 2

Why is it required for complete oxidation (of alcohol to carboxylic acid)?

Answer 2

Vapour is formed which escapes the mixture, but condenses back into a liquid in the condenser
This means that if any alcohol or aldehyde escapes initially, it returns so that it can be oxidised

Question 3

Anti-bumping granules are placed in the flask when refluxing. Suggest why these granules stop bumping

Answer 3

Forms smaller bubbles

Question 4

Describe briefly how you could measure the melting point of aspirin

(2 marks)

Answer 4

Sample in capillary/ melting tube

Heat GENTLY/ SLOWLY near melting point

Question 5

Explain why, during re-crystallisation;

1. The sample is dissolved in minimum volume of hot water
2. The solution is filtered hot
3. The filtrate is cooled in ice to form crystals
4. The crystals are washed with cold water, after the crystals are collected by filtration

(5 marks)

Answer 5

1. To obtain a saturated solution and to enable crystallization (2)
2. To remove INSOLUBLE impurities
3. To increase amount of crystals formed
4. Washed with cold water to remove SOLUBLE impurities

Question 6

How do you distinguish between two separate samples of ammonia and methylamine

(2 marks)

Answer 6

Measure pH with pH meter

Methylamine has a higher pH

Question 7

Suggest how the student could check that the mixture had reached equilibrium after one week

(2 marks)

Answer 7

Test for several samples - at least one tested a week

Check that the results have not changed